Process for treatment of fluid reactants



y 4, 1960 J. H. SHAPLEIGH 2,937,923

PROCESS FOR TREATMENT OF FLUID REACTANTS Original Filed Dec. 2, 1949 2 Sheets-Sheet 1 INVENTOR. JAMES H.SHAPLEIGH.

AGENT.

May 24, 1960 J. H. SHAPLEIGH PROCESS FOR TREATMENT OF FLUID REACTANTS Original Filed Dec. 2, 1949 2 Sheets-Sheet 2 FIGS PIC-3.7

F IG.6

INVENTUK JAMES H. SHAPLEIGH.

AGENT.

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PROCESS FOR TREATMENT F FLUID REACTANT Continuation of application Ser. No. 130,841, Dec. 2, 1949. This application Oct. 18, 1957, Ser. No. 691,525

2 Claims. (Cl. 231) This invention relates to the treatment of fluid reactants and more particularly to a tube-type reaction furnace in which fluid reactants may be safely and efliciently treated under conditions of high pressure and high temperature.

At the present time, tube-type furnaces are widely employed for catalytic and noncatalytic treatment of fluid reactants and especially in the treatment of fluid hydrocarbons. In order to promote the various reactions in the reaction tubes of these tube-type furnaces, temperatures as high as from 1500 to 2000 F. are often required. In order to minimize the possibility of tube rupturing or cracking in the heating chamber, the art has heretofore generally found it necessary to operate at substantially atmospheric pressures; i.e., in the range of about 0' to 15 psi. gauge pressure in the hottest portion of the tube. After considerable use, reaction tubes of tube-type furnaces have been found to rupture or crack even at such low pressures due to such factors as design and installation stresses; structure changes in metals employed and particularly in the preferred austenitic-type metals; factors associated with operation such as impingement of high temperature flame or combustion gases on the tube wall and local burning caused by previous coking; shock conditions arising from the presence of undesired condensates resulting from boiling or priming; etc.

If one or more of the reaction tubes crack or rupture during high temperature-low pressure operations, the result is a burning of the effluent gas in the combustion space around the tubes. This burning under conditions at low pressure is generally insufficient to cause any substantial hazard or even appreciable damage to the adjacent tubes. Under conditions of high pressure and high temperature, however, the frequency of tube rupturing or cracking is increased. Moreover, tube failures at high pressure are more likely to take the form of violent blowouts which may seriously damage the entire furnace unit and present a hazard to operating. personnel. Furthermore, under high pressure conditions the reaction tubes themselves contain more gas and the systems on both input and output ends of the reaction tubes contain large volumes of pressurized fluid which are available to feed a tube-break.

In View of these and other hazards accompanying high pressure-high temperature operations, the art has found it undesirable to conduct such reactions in tube-type furnaces unless either or both temperature and pressure are kept relatively low. For example, high pressure coils or banks of tubes have been successfully employed in refining petroleum where tube temperatures are usually kept below about 1200 F. Under such conditions, the rupture-stress of the metal gives a practical apparatus life. However, failures still occur and a degree of hazard is still present regardless of the metal strength employed. In contrast to petroleum refining, tube temperatures of from 1500 to 1800 F. are commonly emaes 2,937,923 Patented May 24, 1960 ployed in the catalytic cracking of natural gas and other fluid hydrocarbons to produce hydrogen. Some reactions are actually carried out at tube temperatures of 2000 F. at which temperature there is practically no stress-rupture data available to form a basis for the design of a safe and satisfactory pressure apparatus. As a result, the art has decided that due to great potential danger of tube rupture and the resulting hazards, pressures above substantially atmospheric are to be avoided as impractical and dangerous in high temperature reactions conducted in tube-type furnaces. This recognition of potential hazard has, in the absence of any solution to the problem, effectively arrested the development of the art in the field of the high pressure-high temperature reaction of fluid reactants in the preferred tubetype reaction furnace.

Actually there are many advantages of a high pressurehigh temperature system which would be most attractive if it could be seen that such a system would be capable of efficient operation Without substantial hazard. For example, many reactions require the use of pressurized synthesis gas as a reactant. In its present state the art finds it necessary with tube-type furnaces to first produce the synthesis gas and subsequently compress it to the desired pressure. In the case of direct production of pressurized synthesis gas from natural gas, it is the general practice to react the gas with oxygen at a pressure of 200-300 p.s.i. in an internally insulated pressure chamber to convert it to a pressurized synthesis gas. This process involves high investment in pressurized reactor equipment and the use of expensive oxygen or an expensive oxygen-producing process.

If high pressure-high temperature conditions could be simultaneously employed in a tube-type reaction furnace, pressurized synthesis gases could be produced directly by reacting pressurized natural gas, or other fluid hydrocarbon, with steam, carbon dioxide, or other suitable oxygen-carrying gas. Expensive oxygen-producing facilities could thus be eliminated. Since the fluid hydrocarbon could be introduced into the reaction tube at a selected pressure substantially above atmospheric, subsequent compression of the product gas could be entirely eliminated or at least substantially reduced. Furthermore, all of the advantages incident to carrying out reactions at elevated pressures and temperatures could be realized. Greatly enhanced efficiencies would result since under conditions of high temperature and pressure, reaction rate is increased While maintaining the same amount of heating surface.

An object of the present invention, therefore, is a tube-type reaction furnace in which fluid reactants, and particularly fluid hydrocarbons, may be catalytically or noncatalytically treated under conditions of high temperature and high pressure with enhanced elliciency and safety. A further object of the invention is such a tube-type reaction furnace in which more than one fluid reactant may be simultaneously but separately treated. Other objects of the invention will appear hereinafter, the novel features and combinations being set forth in the appended claims.

Generally described, the present invention is a tubetype reaction furnace for the treatment of pressurized fluid reactants having in combination a heating chamber, at least one elongated metallic reaction tube disposed in the heating chamber, an outer metallic tube disposed about a substantial portion of each reaction tube in the region of maximum stress Within the heating chamber, said outer tube being in fluid-impervious relationship with both the reaction tube and the heating chamber, means for delivering pressurized fluid reactants to each reaction tube, and means for removing pressurized reaction products from each reaction tube.

Also included in the present invention is a process for the treatment of fluid reactants under conditions of high temperature and high pressure which comprises passing fluid reactants through a reaction zone at a pressure substantially above atmospheric pressure, introducing a substantially inert gas into a confinement zone disposed about the reaction zone in fluid-impervious relationship therewith, and heating the reaction zone to a predetermined temperature by means disposed externally of the confinement zone and in fluid-impervious relationship therewith. Preferably, the substantially inert gas is maintained at a pressure substantially above atmospheric pressure but below the pressure of the fluid reactants in the reaction zone.

The furnace of the invention may contain a single reaction tube within each outer tube or may have a plurality of reaction tubes disposed concentrically or in spaced relationship with each otherrand the wall of the outer tube. Preferably, the outer tubes and the inner reaction tubes will both pass completely through the heating chamber. However, it is also within the scope of the invention that both the outer tube and the inner reaction tube or tubes be completely contained within the heating chamber. It is further preferred that the outer tube and the reaction tube or tubes be coextensive within the heating chamber whether or not either or both extend through one or both ends of the heating chamber. However, it is also within the purview of the invention that the outer tube should only be disposed about a selected portion of the reaction tube or tubes in the regions of maximum stress within the heating chamber where a tube rupture is most likely to occur under high temperature-high pressure conditions. For example, some metals are weakened by the slow formation of sigma phase. It has been found that sigma formation in the reaction tubes of tube-type furnaces is not confined only to the region where the tubes are at temperatures conducive to sigma formation. To the contrary, the sigma phase has been encountered in other portions of the reaction tubes which are normally maintained at substantially lower temperatures, possibly because those portions of the tubes have been temporarily but repeatedly exposed to abnormal temperatures due to operating abnormalities. Consequently, it may be desirable, in accordance with this invention, to protect only those portions of the reaction tubes which are most frequently subjected to such abnormalities. Therefore, with reference to the embodiments of this invention, it will be understood that a reaction tube or a portion thereof susceptible to rupture will be surrounded by an outer tube which is in fluid-impervious relationship with the heating chamber.

Either or both ends of the outer tube may be in com munication with the atmosphere exteriorly of the :furnace. Similarly, either or both ends of the outer tube may contain, exteriorly of the furnace, rupturable means such as blowout plugs or portions of relative weakness which will rupture or be expelled and allow excessive internal pressure due to a ruptured reaction tube to exhaust to the atmosphere either at the point of the rupturable member or along an exhaust line. ing to a preferred embodiment of the invention, the interior of the outer tube is in communication with a first valving means to selectively'discontinue or otherwise control the flow of fluid reactants into the reaction tubes and is in communication with a second valving means to prevent or otherwise. control the backflow of pressurized reaction gases into the ruptured reaction tube. Thus, when a tube failure occurs, the ruptured tube may be automatically and completely isolated singly or in combination with other tubes from the remainder of the system. Alternatively, suitable valving mechanisms may be employed to exhaust escaping gases to the atmosphere or to control only the flow of fluid hyd o rbons to the reaction tube while allowing the flow Accordof steam or other inert gas being employed to continue. In this way, the blanketing effect of the inert gas may be effectively utilized as an additional safety measure.

In accordance with the preferred embodiment of the invention, the outer tube is associated with means for the introduction into the outer tube of a gas, which is noncombustible and which will not support combustion in admixture with the reactants. Means are also provided for maintaining the gas Within the tube at any desired pressure. The presence of such a gas within the outer tube is very beneficial since if the gas is substantially inert, it will blanket the reactants flowing from a ruptured reaction tube which are often combustible and/ or explosive. In addition, if the gas within the outer tube is maintained at a pressure between atmospheric and the reaction tube pressure, much of the load can be removed from the reaction tube. The presence of a substantially inert gas in the outer tube also prevents, or at least greatly diminishes, carburization, sulphidation, or sulphation of the outer wall of the reaction tubes, or the formation of nitrides and oxide scales on the outer walls of the tubes. All of these conditions are known to greatly reduce the stress-rupture value of thin-walled reaction tubes and their elimination or diminuation adds greatly to reaction tube life. This is especially true under high pressure-high temperature conditions where the limited working margin under such conditions necessitates, as far as possible, the avoidance of any condition tending to disrupt the uniformity of the reaction. Examples of gases which may be employed within the outer tube include steam, carbon dioxide, flue gas of low oxygen content, nitrogen, and argon.

The inner and outer tubes may be supported and maintained in their relative positions externally of the heating zone by securing their extremities to suitable supporting members. The reaction tube may also be supported by ribs disposed between the inner and outer tubes and in contact therewith. In like manner, the reaction tubes themselves may be constructed with internal strengthening members disposed longitudinally thereof and secured to the tubes inner surface.

While heat may be supplied to the interior of the furnace by any suitable means known to the art, the use of spaced gas burners in accordance with the disclosure of US. Re. 21,521 is preferred since this particular type of heating means provides a heating chamber or zone wherein positive control can be exercised.

Having generally described the invention, a more detailed description of several specific embodiments thereof will be given for illustrative purposes with reference to the accompanying drawings in which like symbols refer to like parts wherever they occur.

Fig. 1 is a part sectional, part elevational view of a preferred embodiment of a tube-type cracking furnace according to the present invention. Figs. 2, 3, 4 and 5 are diagrammatic views of additional embodiments of tube units which may be employed in accordance with the invention. Figs. 6, 7 and 8 are sectional end views of further embodiments of tube units which may be employed in accordance with the invention.

Referring to Fig. l of the drawing which illustrates a preferred embodiment of the invention, a furnace '10 is constructed from refractory fire brick. Passing longitudinally through the heating chamber of the furnace to are outer metallic tubes 11 which are suspended from a plurality of spring-like supporting means, as represented by the support means 12, which are connected to flanges 13 atlixed to the exterior surface of the tubes 11. Fluidimpervious joints are provided through the upper furnace wall byisealing rings 14 and asbestos packing rings 15. concentrically disposed within each outer tube 11 is a steel alloy reaction tube 16. The reaction tube 16 is supported by means of a weld 17 which joins the tubes 11 and 16 in fluid-impervious relationship above the furnace arch 18. T e pper end of each react on tube 6.

is closed by means of a sealing plate 19. The lower ends ofthe outer tubes 11 and the reaction tubes 16 are sealed and positioned by means of a grooved plate 20 and bolts 21. The annular space 22 formed between the outer tube 11 and the inner reaction tube 16 is in communication with an exhaust tube 23 through flexible metal conduit 24. Exhaust tube 23 is supported by a support member 25 and is in communication with both sets of outer tubes 11. Disposed in the upper end of the exhaust tube 23 is an adjustable pressure release valve 26. A line 27 connects the exhaust tube 23 with a control mechanism 28, the function of which is hereinafter described.

Inlet lines 29 conduct the fluid reactants into the upper portions of the reaction tubes 16. A pressure-actuated cutoff valve 30 is disposed in each inlet line 29 and is in communication with the control mechanism 28 through line 31. The lower ends of the reaction tubes 16 which project below the furnace hearth 32 are in communication with headers 33 through lines 34. Disposed in each of the lines 34 is a pressure-actuated cutofi valve 35 which is also in communication with the control mechanism 28 through lines 36 and 31. The lower end of each of the outer tubes 11 is constructed with an expansion joint 37. The ends of the outer tubes 11 and reaction tubes 16 extending below the furnace hearth 32 are enclosed in insulating jackets 33. Lines 39 lead to the annular space 22 between the outer tubes 11 and the reaction tubes 16 and are employed for the introduction into the annular space 22. of gas which is noncombustible and is incapable of supporting combustion. Lines 39 may also be employed to purge the annular space 22, if desired.

Valve 3!} may be adapted to control only a fluid reactant capable of combustion while allowing the flow of an inert or dampening fluid, such as steam, to continue. Likewise valve 35 may serve as a complete cutoif or it may be adapted to cut off the defective tube from downstream pressurized gas and to vent the upstream portion or" the pressurized system to the atmosphere. Valves 30 and 35 may be located as shown or at selected points in the pressurized system to function as described. Control mechanism 28 may be an electrical or mechanical device of which numerous types are available, and in addition to the functions described above, may be employed to control master input and output to the entire unit, to open exhaust vents and to control pressure-producing equipment such as pumps or compressors.

In operation, the furnace is first fired by suitable means (not shown) and the reaction tubes 16 are brought to the desired temperature. The furnace heats the outer walls of the outer tubes 11 which in turn heat the reaction tubes 16 by radiation. The annular space 22 is filled with steam or other gas which is noncombustible or which will not support combustion in admixture with the reactants. Pressurized fluid reactants such as a fluid hydrocarbon and steam are now admitted to the reaction tubes through inlet lines 29 and the product gases of the reaction are withdrawn through the outlet lines 34 to the headers 33. If a rupture occurs in the reaction tubes 16, the pressure at once increases in the annular space 22 between the reaction tube 16 and the outer tube 11. This increase in pressure is transmitted to the exhaust tube 23 through the flexible metal conduit 24. The control mechanism 23 which is set at a predetermined pressure activates valves 30 and 35 disposed in the inlet line 29 and outlet line 34, respectively, whereupon the inlet line 2% and the outlet line 34- are closed,

In Fig. 2, a reaction tube is concentrically disposed within a longer outer tube 51. Both the reaction tube 50 and the outer tube 51 are suspended in a heating chamber 52 by means similar to that described for Fig. 1. The reaction tube 50, the outer tube 51 and the heating chamber 52 are all in fluid-impervious relationship with each other. Fluid reactants are introduced into the top of the reaction tube 54} by an inlet line 53 and the reaction products are withdrawn at the bottom of the reaction tube 50 through an outlet line 54. Lines 55 and 55 are in communication with the annular space 57 be between the reaction tube 50 and the outer tube 51. Substantially inert gas may be introduced into the annular space 57 through either line 55 or 56 and may be maintained at any desired pressure. The annular space 57 may also be purged by passing inert gas into one of lines 55 and 56 and out the other. An exhaust line 58 containing a pressure release valve 59 leads from the annular space 57 to the atmosphere. Alternatively, exhaust line 58 may be in communication with a control system as described in conjunction with Fig. 1.

In Fig. 3, a reaction tube 66 passes completely through a heating chamber 61. Au outer tube 62 is concentrically disposed about a portion of the reaction tube 60 and also extends through the upper wall of the heating cham ber 61. The reaction tube 60, the heating chamber 61, and the outer tube 62 are all in fluid-impervious relationship with each other. Fluid reactants are introduced into the top of the reaction tube as through an inlet line 63 and reaction products are withdrawn from the bottom of the reaction tube 61 through an outlet line 64. Lines s5 and 66 are in communication with the annular space 67 between the reaction tube 651 and the outer tube 62. Substantially inert gas may be introduced into the annular space 67 through either line or line 66 and may be maintained at any desired pressure. The annular space 6'7 may also be purged by passing inert gas in one of lines 65 or 66 and out the other. An exhaust line 68 containing a pressure release valve 69 leads from the annular space 67 to the atmosphere. Alternately, exhaust line 68 may be in communication with a control system as described in conjunction with Fig. 1.

In Fig. 4, a single reaction tube 7%) is concentrically disposed within a shorter outer metallic tube 71. The tubes 71) and 71 both pass completely through a heating chamber '72. The closed end of the reaction tube 76 extends a short distance from the end of the outer tube 71 and the two are joined in fluid-impervious relationship. The annular space 73 between the tubes and 71 is sealed ofl at the upper end of the outer tube 71 by a frangible disc 74 designed to be ruptured at a predetermined pressure within the annular space 73. Below the heating chamber 72 an annular corrugated member 75 is sealed to the lower end of the outer tube 71 and to the outer surface of the reaction tube 70. The corrugated section 75 allows for any differential in expansion between the reaction tube 70 and the outer tube 71. Lines 76 and 77 are in communication with the annular space 73 between the reaction tube 71 and the outer tube 71. Substantially inert gas may be introduced into the annular space 73 through either of the lines 76 and '77 and may be maintained at any desired pressure. The annular space 73 may also be purged by passing an inert gas into the space through one of lines 76 and 77 and out the other.

Pressurized fluid reactants are introduced to the upper end of the reaction tube 70 through inlet line 78. The fluid reactants pass through tube 70 and react in the region surrounded by the combustion chamber 72. The product gases are led from the bottom of the reaction tube through an outlet line '79. if the reaction tube 70 ruptures, the gases from the reaction tube 70 flow into the annular space 73 between'the reaction tube 70 and the outer tube '71. At a predetermined pressure, the frangible disc 74 ruptures and the gases escape to the 7 atmosphere or along 'a specially provided exhaust line (not shown).

In Fig. is shown a modification of the tube unit shown in Fig. 1. In the apparatus of Fig. 5, a reaction tube 80, a reaction tube 81, and an outer tube 82 are concentrically disposed and passed completely through a heating chamber 83. The three tubes are joined together in fluid-impervious relationship above the heating chamher 83. Below the heating chamber 83, the outer tube 82 is joined to the outer reaction tube 81 in fluid-impervious relationship by an annular corrugated member 84 and the outer reaction tube 81 is in turn joined to the inner reaction tube 80 in fluid-impervious relationship by an annular corrugated member 85.

Pressurized fluid reactants are introduced into the inner reaction tube 80 through the feed line 86. A pressure cutoir valve 87 is disposed in feed line 86. The same or different pressurized fluid reactants are introduced into the outer reaction tube 81 through feed line 88 in which is disposed a pressure cutoff valve 89. An exhaust line 90 leads from the annular space 91 between the outer tube 32 and the reaction tube 81 to a control mechanism 92. Mechanism 92 and valve 89 are in communication through a line 93. Lines 94 and 95 are in communication with the annular space 91 between outer reaction tube 31 and the outer tube 82. A substantially inert gas may be introduced into the anular space 91 through either of lines 94 and 95. Annular space 91 may also be purged by passing inert gas into the annular space through one of lines 94 and 95 and out through the other. Below the heating chamber 83, an outlet line 96 leads from the outer reaction tube 81 through valves 97 and 98. An outlet line 99 leads from the lower end of the inner reaction tube 80 through a valve 100. Control mechanism 92 is in communication with inlet valves 87 and 89 through lines 101 and 93 respectively. Control mechanism 92 is in communication with outlet valve 98 through line 162 and with outlet valve 100 through lines 102 and 103. Valve 97 in line 96 is also in communication with mechanism 92 through line 1114.

If during operation of the apparatus shown in Fig. 5 the outer reaction tube 81 cracks, internal pressure builds up in the annular space 91 between the outer tube 82 and the outer reaction tube 81. At a predetermined pressure, control mechanism 92 is activated and pressurized gas is allowed to flow from the annular space 91 into lines 93, -1, 1% and 103 to close, respectively, inlet valves 89 and 87 and outlet valves 98 and 109. If, on the other hand, the reaction tube 89 ruptures, the pressure in reaction tube 81 will be either raised or lowered depending upon the relative pressures maintained in the tubes 80 and 81. At a predetermined pressure in tube 81, the valve 97 in outlet line 96 activates control mechanism 92 and pressurized gas is allowed to flow from tube 81 through line 104, through control mechanism 92 and lines 93, 101, 102 and 103 to close inlet valves 87 and 89 and outlet valves 98 and 100 as described above. Consequently, whichever of the reaction tubes ruptures, the concentric disposition of the reaction tubes prevents the flammable and/or explosive gases from being released into, the interior of the furnace. As in the other units illustrated, a substantially inert gas, such as nitrogen, carbon dioxide, or steam, may be introduced into the annular space 91 and may be maintained at any desirable pressure.

In Fig. 6 is shown a modification of a tube unit in accordance with the invention in which three reaction tubes 110 are longitudinally disposed within an outer tube 111 in spaced relationship with each other and with the inner wall of the outer tube. The reaction tubes 110 are heated by radiation from the outer tube 111 which is in turn heated by a furnace such as described in conjunction with Fig. l.

In Fig. 7, a single reaction tube 120 is concentrically disposed within an outer tube 121. In addition to any support means employed at either end of the tube, ribs 122 are longitudinally disposed between the outer surface of the tube 120 and the inner surface of tube 121. These ribs reduce distortion of the reaction tube 120 during use and thereby serve to reduce the stresses present in the assembly. The ribs 122 may be independent ele ments secured to either or both the outside of the reaction tube 120 or the inside of the outer tube 121. Alternatively, the tube 120 or 121 may be cast with the vertical ribs as an integral part thereof or the entire structure of tube 120, tube 121, and ribs 122 may be cast as an integral unit.

In Fig. 8, a reaction tube 130 is concentrically disposed within an outer tube 131. Ribs 132 are disposed between the tubes 13% and 131. The reaction tube 130 is divided into sections by a cross-like member 133, each extremity of which is secured to the inner wall of the tube 130. The inner tube may be made by casting as an integral unit or else may be fabricated from separate segments, if desired. The member 133 serves to strengthon the reaction tube 139 and to increase heat transfer surface. Members may be employed which divide the reaction tube into any number of sections as long as objectionable resistance to gas flow does not result. As in the case of the unit shown in Fig. 7', the entire structure shown in Fig. 8 may be cast as an integral unit.

It will be seen, therefore, that a tube-type reaction furnace constructed in accordance with the invention makes possible the treatment of fluid reactants, such as hydrocarbons, under conditions of high temperature and high pressure with enhanced safety. However, the disposition of one or more reaction tubes within an outer tube, in accordance with the invention, should not be considered as beneficial solely as a safety measure. In the tube-type reaction furnaces in accordance with the invention, the life of the reaction tubes is actually greatly prolonged since the heating of the reaction tubes by radiation from the outer tubes is considerably more uniform than in prior art apparatus where the reaction tubes are heated directly. Even though the heat applied to the outer tube is somewhat irregular, the tube serves as a balance wheel in heat transfer and the irregularities externally applied to the outer tube are distributed to produce a smooth flow of radiant heat to the reaction tubes. When operating at high pressure and high temperature, a uniform tube temperature is greatly to be desired since the margin of safety between the stress-rupture values for a given operating temperature is often small. Furthermore, the outer tube acts as a butter and protects the pressure reaction tubes from injury which would ordinarily result from abnormalities of firing and flame impingement which are major factors in causing tube rupture in currently used tube-type furnaces. In addition, the outer tube protects adjacent tubes from the jetting and flame impingement which has heretofore resulted from the rupturing of a near-by tube and which quickly results in the failure of adjacent tubes under high temperature-high pressure conditions.

Where the combustion gases contain sulfur, the outer tube protects the reaction tubes from sulfur corrosion.

Where, as is preferred, the outer tube contains an inert gas, the formation 'of oxide scale on the reaction tube is eliminated or at least minimized. I

An additional advantage apart from the apparatus itself and the danger accompanying explosion lies in the fact that discomfort and danger to operating personnel caused by polution of the atmosphere with low oxygen content gases or gases containing carbon monoxide can be completely eliminated.

The tubes employed in accordance with the present invention can be made of selected materials presently used and designed to obtain the longest service life in accordance with the present knowledge of the art. reaction tubes of tube-type furnaces have generally been constructed from an austenitic type of steel. Type 310 metal is widely employed and some cast steel tubes have The 9 been used. Type 310 metal stabilized with about 1% of columbium is one preferred metal of construction for the tubes in accordance with the invention. The inclusion of from about 3-6% of tungsten has also been found to give increased strength.

While most tube-type furnaces employ vertically disposed reaction tubes and While the invention has been specifically illustrated with embodiments in which the reaction tubes and outer tubes are vertically disposed, the invention is not to be considered as limited to vertically disposed tubes. Actually, as will be apparent to those skilled in the art, the reaction tubes may be horizontally or diagonally disposed in the heating chamber and may be in banks, U-bends, or coils.

The annular corrugated members and expansion joints which have been shown are preferably made from a scale-resistant metal in such a manner that the structure has suflicient elasticity to compensate for expansion differential between the tubes. However, the invention is not restricted to the use. of annular corrugated metallic members. Although such corrugated expansion joints are preferred, other methods of compensating for expansion differential are known and may be employed.

It is also within the scope of the invention that fluid reactants may be furnished to the reaction tubes by means of suitable manifolds instead of through individual feed lines as shown in the specific illustrations.

The apparatus of the invention may be employed for either catalytic or noncatalytic reactions or when employing a plurality of reaction tubes as shown in Figs. 5 and 6,

catalytic and noncatalytic reactions can actually be simultaneously carried out in the different tubes in the same apparatus. When a furnace according to the invention is employed for a catalytic reaction, the catalyst may be positioned in the reaction tubes in any suitable manner known to the art. While furnaces in accordance with the invention are primarily useful for the treatment of fluid hydrocarbons and particularly for the production of hydrogen, synthesis gas and olefin gas by catalytic and noncatalytic treatment of fluid hydrocarbons, the invention has general utility in the treatment of fluid reactants.

Since many modifications which do not depart from the scope of the invention will be apparent to those skilled in the art, the invention is to be limited only by the scope of the appended claims.

This application is a continuation of my application Serial No. 130,841, filed December 2, 1949, now abandoned.

What I claim and desire to protect by Letters Patent is:

1. In the treatment of fluid reactants in a tube-type furnace under conditions of high pressure and high temperature, the process which comprises passing fluid react ants through a reaction zone within a metallic reaction tube at a pressure of at least about 200 p.s.i., introducing an inert gas into a confinement zone disposed about the reaction zone in fluid-impervious relationship therewith, said inert gas being one which is substantially inert with respect to the fluid reactants in the reaction zone, maintaining said inert gas at substantially atmospheric pressure, and heating the reaction zone to a predetermined temperature by means disposed externally of the confinement zone and in fluid-impervious relationship therewith.

2. The process of claim 1 wherein the confinement zone is in communication with a control mechanism which is set at a predetermined pressure above the normal pressure existing in the confinement zone but below the pressure existing in the reaction zone to discontinue the flow of fluid reactants into the reaction zone and to prevent any backflow of reaction products into the reaction zone such that when a rupture in the wall of the metallic reaction tube occurs and the pressure in the confinement zone builds up to the aforesaid predetermined pressure the fiow of reactants into the reaction zone is discontinued and any backflow of the reaction products into the reac tion zone is prevented.

References Cited in the file of this patent UNITED STATES PATENTS 1,286,135 Somermeier Nov. 26, 1918 1,358,383 Metzger Nov. 9, 1920 2,545,384 Rehrig Mar. 13, 1951 

1. IN THE TREATMENT OF FLUID REACTANTS IN A TUBE-TYPE FURNACE UNDER CONDITIONS OF HIGH PRESSURE AND HIGH TEMPERATURE, THE PROCESS WHICH COMPRISES PASSING FLUID REACTANTS THROUGH A REACTION ZONE WITHIN A METALLIC REACTION TUBE AT A PRESSURE OF ATLEAST ABOUT 200 P.S.I., INTRODUCING AN INERT GAS INTO A CONFINEMENT ZONE DISPOSED ABOUT THE REACTION ZONE IN FLUID-IMPERVIOUS RELATIONSHIP THEREWITH, SAID INERT GAS BEING ONE WHICH IS SUBSTANTIALLY INERT WITH RESPECT TO THE FLUID REACTANTS IN THE REACTION ZONE, MAINTAINING SAID INERT GAS AT SUBSTANTIALLY ATMOSPHERIC PRESSURE, AND HEATING THE REACTION ZONE TO A PREDETERMINED TEMPERATURE BY MEANS DISPOSED EXTERNALLY OF THE CONFINEMENT ZONE AND IN FLUID-IMPERVIOUS RELATIONSHIP THEREWITH. 